In radio communication, when an obstacle, such as a building, exists on a propagation path of a radio wave, a reception level is lowered. For this reason, there has been a technique for transmitting a reflected wave to a location difficult for a radio wave to reach by disposing a reflection plate (reflector) at a high place, where a height of the high place is greater than or equal to that of the building. In a case where a radio wave is reflected by a reflector, when an angle of incidence of the radio wave in a vertical plane is relatively small, it is difficult for the reflector to direct the radio wave to a desired direction (FIG. 1). That is because, in general, an angle of incidence of a radio wave is equal to an angle of reflection. To address this problem, it can be considered to incline the reflector, so that the reflector faces a ground surface. The angle of incidence and the angle of reflection relative to the reflector can be enlarged by doing so. In this manner, an incident wave can be directed to a desired direction. However, from a viewpoint of safety, it is not preferable to incline the reflector toward the ground surface, because the reflector is disposed at the high place comparable to the height of the building that blocks the radio wave. From such a point of view, a reflector has been desired such that an angle of incidence of a radio wave is different from an angle of reflection of the radio wave. Namely, a reflector has been desired such that, even if an angle of incidence is relatively small, a reflected wave can be directed to a desired direction. A conventional reflector has been described in Non-Patent Document 1, for example. In the reflector, an angle of reflection of a radio wave is attempted to be controlled by causing plural elements to form corresponding reflected waves having a predetermined reflection phase. Since this type of reflector includes plural elements, this type of reflector may be referred to as a “reflectarray.”
In a mobile communication system, when communication quality in an area is to be improved by using a reflectarray, it can be considered to enlarge an area of the reflectarray, so that a reception level of a reflected wave becomes greater. However, when a size or the area of the reflectarray is simply enlarged, a beam width of the reflected wave becomes smaller, though the intensity of the reflected wave is increased. A problem is that the area in which communication quality can be improved becomes narrow. When the size of the reflectarray is small, the beam width of the reflected wave becomes relatively large. Unfortunately, the reception level of the reflected wave becomes small.
As for such problems, an attempt has been made to reflect an incident radio wave in plural directions (Non-Patent Document 2). Unfortunately, the method described in Non-Patent Document 2 is not for directing the reflected wave in an arbitrarily desired direction. Thus, it is possible that, in an area where a radio wave environment is to be improved, the communication quality is not sufficiently improved.